The present invention relates generally to linear motion damping devices, and particularly to those devices adapted for use as shock absorbers and impact energy absorbers employed in safety bumper assemblies for automobiles.
In the area of damper devices employed to lessen the impact of sudden linear motion, the conventional construction has comprised the provision of a sealed, fluid filled cylinder containing therewithin a piston mounted upon a rod and reciprocable within the cylinder. Such devices, commonly known as shock absorbers, find application in a wide variety of instances, including the reduction of vibration in industrial machinery, and motor vehicles. In the instance where the shock absorber is installed in a motor vehicle, the generally larger diameter cylinder portion is pivotally mounted to the upper frame of the vehicle, while the smaller diameter piston and rod project oppositely from the cylinder and are fastened to the wheel assembly. Thus, vertical movement of the wheel assembly, as in the instance where an uneven road surface is encountered, causes the piston to travel upward within the cylinder, where it encounters resistance from a spring or from the pressurized fluid contained therein. The axial movement of the piston is limited by the oppositely directed axial pressure offered by the spring or compressed fluid within the cylinder.
The construction described above has been in use for many years, and with relatively minor modification, remains unchanged to the present in its reliance upon the axial application of fluid pressure to limit linear motion. While this design has stood the test of time, it nonetheless suffers from certain defects. Specifically, the shock absorbers employed in automotive applications, despite improvements in piston and fluid seal design, and the fluids themselves, exhibit a limited durability and useful life in service. Particularly in the instance where the vehicle in question is driven frequently over roads lying in serius disrepair due to the severity of winter conditions, the shock absorbers are subjected to severe, repeated impact as the vehicle travels over roads covered with unrepaired pot holes. This type of abuse quickly degrades the fluid seals surrounding the piston, with the result that the shock absorber is no longer capable of maintaining the fluid pressure necessary to offer the desired resistance to linear motion. Additonally, conventional shock absorbers offer a fixed resistance to shock, i.e. the resistance does not vary even though the shocks to which they are subjected vary from very minor to quite severe.
Applicant has considered the problems raised by the above phenomenon and has determined that the surface area presented by the transverse face of the piston is inadequate to withstand the repeated impacts of daily use, as excessive pressure per unit area is forced to impinge thereupon. Applicant determined that a more desirable damper design would attempt to provide greater surface area within present size requirements, for the reception of fluid resistance to increase the impact resistance capacity of the damper unit.
As noted above, the conventionally constructed shock absorber has found recent application as part of energy absorbing bumper systems which are now required by law to be installed on all motor vehicles manufactured for use and sale in the United States. In this connection, U.S. Pat. No. 3,829,142 to Bommerito and U.S. Pat. No. 4,061,386 to Cupik, the latter referring to U.S. Pat. No. 3,794,310 to Mewhinney, are representative of the incorporation of the basic shock absorber design discussed above, with minor modification, as part of the energy absorbing unit employed within the bumper assemblies.
In U.S. Pat. No. 3,486,776 issued to Applicant on Dec. 30, 1969, a clutch or brake assembly is disclosed for the purpose of curtailing the rotation of a roller on a shaft by the exertion of laterally directed fluid pressure applied between the adjacent surfaces of the shaft and the roller, to frictionally engage the adjacent surface to impede the rotation of one relative to the other. The application of fluid pressure to an expansible surface to frictionally engage an adjacent rotating surface in the manner of a clutch or a brake, is acknowledged in the prior art, as exemplified by U.S. Pat. No. 2,093,281 to Kreuser, U.S. Pat. No. 2,111,422 to Fawick, and more recently, in U.S. Pat. No. 4,093,052 to Falk. In all of the foregoing instances, lateral fluid pressure is manually applied to achieve extended frictional engagement, in most instances for the purpose of achieving the rotation of two separate members in union, or to curtail the motion of both members entirely. No disclosure has been found that would suggest that the exertion of lateral fluid pressure would be effective in a damper for the control of linear motion.